MAMMALS 



209 



Why does a whale need large lungs ? The tail of a whale 



is horizontal instead 

 I of vertical, that it may 

 S steer upward rapidly 

 1 from the depths when 

 needing to breathe. 

 The teeth of some 

 FIG. 379- -DOLPHIN. whales do not cut the 



gum, but are reabsorbed and are replaced by horny plates 

 of " whalebone," which act as strainers. Give evidence, 

 from the flippers, lungs, and other organs, that the whale 

 is descended from a land mammal (Fig. 397). Compare 

 the whale with a typical land mammal, as the dog, and 

 enumerate the specializations of the whale for living in 

 water. What change took place in the general form of the 

 body ? It is believed that on account of scarcity of food 

 the land ancestors of the whale, hundreds of thousands of 

 years ago, took to living upon fish, etc., and, gradually be- 

 coming swimmers and divers, lost the power of locomotion 

 on land. Order Why ? 



Elephants are rapidly becoming extinct because of the 

 value of their 

 ivory tusks. 

 Whales also 

 furnish valua- 

 ble products, 

 but they will 

 probably exist 

 much longer. 

 Why? 



The manatees and dugongs (sea cows) are a closely re- 

 lated order living upon water plants, and hence living close 

 to shore and in the mouths of rivers. Order Why ? 





FIG. 380. MANATEE, or sea cow ; it lives near the shore 

 and eats seaweed. (Florida to Brazil.) 



